Crown control compensation controlling method in multiple roll mill

ABSTRACT

A crown control compensation controlling method in a multiple roll mill, in which a variation of rolling load caused by crown control is obtained from a crown control quantity. A wedge type hydraulic reduction device is operated according to the variation of rolling load to thereby cancel such rolling load variation. Both an automatic gauge control (AGC) and an automatic shape control (AFC) can be attained while preventing a change in plate thickness caused by crown control.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a crown control compensationcontrolling method capable of automatically compensating for variationsin plate thickness caused by crown control and effecting a stablecontrol in a multiple roll mill for rolling thin plates such asnonferrous metals and special steels.

2. Description of the Prior Art

As an actuator for controlling the shape of a rolling stock being rolledby a multiple roll mill there is a crown control device. It is knownthat, if this device is operated, there will arise a change in roll gap,which causes a variation in plate thickness.

Therefore, where such crown control device is operated to control theshape of a rolling stock, it is necessary to perform operationsgradually in consideration of a response from a thickness gauge so asnot to exert a bad influence on the plate thickness.

On the other hand, a wedge type hydraulic reduction device has beenapplied to a multiple roll mill. This device makes a high-speed controlfor roll gap and effects an automatic plate thickness control asdisclosed in Japanese Patent Laid-Open Publication No. 9707/83. For thisautomatic plate thickness controller there is adopted a constant gapcontrol or a feed forward control to obtain products with a highaccuracy of plate thickness.

According to the prior art, however, variations in plate thicknesscaused by crown control are corrected only by feedback of a thicknessgauge monitor, so during the period corresponding to the delay time ofthe feedback, the plate thickness becomes off-gauge, thus making itimpossible to effect a high-speed control for obtaining a rolled productwhich is satisfactory in both shape and thickness.

SUMMARY OF THE INVENTION

According to the present invention, which has been accomplished in viewof the above problem, there is provided a crown control compensationcontrolling method in a multiple roll mill capable of cancelling avariation in plate thickness caused by crown automatically andreal-timewise to realize both a high-speed AGC (automatic gauge control)and a high-speed AFC (automatic flatness control) at the same time.Accordingly, the subject method produces a product having a highaccuracy of thickness and a good shape.

In order to achieve the above-mentioned object, the crown controlcompensation controlling method in a multiple roll mill of the presentinvention is characterized in that a variation in rolling load caused bycrown control is determined from a crown control quantity, and a wedgetype hydraulic reduction device is operated according to such variationin rolling load to thereby cancel the rolling load variation. Bycombining this controlling method with a constant gap control, anautomatic flatness control (AFC) and an automatic gauge control (AGC)for rolling stocks are both obtained, thereby realizing a so-called AFGCsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate an embodiment of the present invention, inwhich:

FIG. 1 is a block diagram showing a concrete construction of the presentinvention combined with a constant gap control; and

FIG. 2 is a rolling characteristic diagram for explanation of theprinciple of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

An embodiment of the present invention will be described hereinunderwith reference to the drawings.

Referring first to FIG. 2, there is illustrated the principle of aconstant gap control in which a rolling load which varies depending on avariation in plate thickness on an incoming side is detected, and theroll gap is corrected by a hydraulic reduction device in accordance withthe detected signal.

It is here assumed that, when a rolling stock having a plate thicknessH₁ on the incoming side is rolled at the initial roll gap S₀, the platethickness on an outgoing side is h₁ and the rolling force is P₀.

When the plate thickness on the incoming side becomes H₂, the platethickness on the outgoing side becomes h₂ if there is no control. At thesame time, the rolling load changes by ΔP from P₀ to P.

Between the rolling load variation ΔP and the plate thickness variationΔh, for the plate thickness variation ΔH on the incoming side, thereexists the following relationship if the mill modulus of the rollingmill is M and the plasticity modulus of the rolling stock is m:

    ΔP=M·Δh                               (1)

If the rolling load variation ΔP is detected by a rolling load meter andthe roll gap is shifted to S (that is, if it is reduced by ΔS) on thebasis of the ΔP, the plate thickness on the outgoing side returns to theoriginal h₁ and the plate thickness variation Δh on the outgoing sidebecomes zero.

Therefore, if a load variation induced by a change of reduction settingis ΔP',

    ΔP'=m·Δh                              (2)

    ΔP=ΔP+ΔP'=-M·ΔS           (3)

wherein ΔP represents the load variation detected by a load cell. Thereason why a negative mark is affixed thereto in the above equation (3)is that the relation between increase/decrease of the roll gap caused byoperation of the control system and increase/decrease of load is aninverse correlation.

If ΔP' and Δh are cancelled from the above equations (1), (2) and (3),##EQU1##

However, since it is impossible for the rolling load cell to detect onlythe load variation ΔP caused by a change in characteristic of therolling stock on the incoming side and disregard the load variation ΔP'induced by a change of the reduction setting, the load cell alwaysdetects ΔP. Therefore, a direct use of the equation (4) in the controlis impossible.

That is, if control is made in accordance with the equation (4),##EQU2## Thus, an excess control results.

To prevent this excess control, it is necessary to draw out only theload variation ΔP. Therefore, it is necessary to predict the loadvariation ΔP' induced by a change of reduction setting.

If the load variation ΔP and the variation of plate thickness Δh on theoutgoing side are cancelled from the equations (1), (2) and (3),##EQU3##

The left side of the equation (5) represents a rate of change in rollingload induced when the reduction setting is varied manually. Thus, bygiving a certain amount of variation in reduction setting manually for avery short time, for example at the beginning of rolling, and actuallymeasuring a rolling load variation at that time, there can be obtained##EQU4## as a measured value.

If this measured value is K₂, the equation (4) can be written asfollows: ##EQU5##

Thus, an optimum control is effected by dynamically offsetting theexcess control based on the load variation ΔP' induced by the roll gapvariation ΔS while performing a reduction control for the ΔS.

The crown control compensation controlling method in a multiple rollmill according to this embodiment of the invention will now be describedon the basis of the above constant gap control method and with referenceto FIG. 1.

The thick line portion in the figure represents a crown controlcompensation controller section.

If the number of crown control points is n, then the coefficient ofinfluence of the crown control quantity at each point upon the rollingload can be obtained by an actual measurement at every rolling pass.Influence coefficients at those control points are assumed to be L₁, L₂,. . . L_(n).

Further, if the rolling load variation when crown control is madewithout changing the other conditions at all is ΔP", and if the crowncontrol quantities at the control points are ΔC₁, ΔC₂, . . . ΔC_(n),##EQU6##

The rolling load variation ΔP' caused by the roll gap control with areduction wedge is as follows from the equation (5): ##EQU7##

The rolling load variation ΔP" induced when crown control is made undercontrol of the reduction wedge can be cancelled and eliminated byeffecting the following control automatically:

    ΔP"+ΔP'→0

Thus, the reduction wedge should be controlled so that the roll gapcontrol quantity ΔS becomes as follows: ##EQU8##

The following description is now provided about the combination of thiscrown control compensation controlling method with the constant gapcontrol. It goes without saying that the combination with a feed forwardcontrol can also be made in the same manner.

As referred to in the equation (4), the following is a basic equation ofthe constant gap control: ##EQU9##

Under the compensation control for crown control,

    ΔP=ΔP+ΔP'+ΔP"

If the load variation ΔP' induced by a change of reduction setting isdivided into a portion ΔP₁ ' of the constant gap control and a portionΔP₂ ' of the crown control compensation control in the presentinvention,

    ΔP=ΔP+ΔP.sub.1 '+ΔP.sub.2 '+ΔP"

Since ΔP"+ΔP₂ '→0 under application of the crown control compensationcontrol,

    ΔP=ΔP+ΔP.sub.1 '

Therefore, from the equation (8), the basic equation of the constant gapcontrol becomes as follows: ##EQU10##

If the roll gap control quantity ΔS is divided into a portion ΔS₁ of theconstant gap control and a portion ΔS₂ of the crown control compensationcontrol,

    ΔS=ΔS.sub.1 +ΔS.sub.2                    (9)

From the equation (5), ##EQU11##

From the equation (7), ##EQU12##

And from the equations (9), (10) and (11), ##EQU13##

Thus, the basic equation of the constant gap control becomes as follows:##EQU14##

FIG. 1 illustrates an automaic roll gap control device for implementingthe above method.

In FIG. 1, the numeral 1 denotes a memory for storing an initial value(set rolling load) P₀ of a rolling load P detected by a rolling loaddetector 2, and the numeral 3 denotes an addition point which detects adeviation of the rolling load P actually measured from the set rollingload P₀ provided from the memory 1, namely, a rolling load variation ΔP.Numeral 4 denotes a multiplier for multiplying the crown controlquantities ΔC₁, ΔC₂, . . . ΔC_(n) at the control points by thecoefficients of influence on rolling load, L₁, L₂, . . . L_(n), tocalculate a rolling load variation ΔP; numeral 5 denotes an additionpoint of those calculated values, which outputs a rolling load variationΔP" under crown control to an addition point 6.

The addition point 6 makes subtraction for the rolling load variationΔP" detected under crown control and at the same time makes addition forthe above rolling load variation ΔP and a secondary rolling loadvariation ΔP' which is provided from a later-described multiplier 19,then taking out only the rolling load variation ΔP.

Numeral 7 denotes a multiplier for muliplying the rolling load variationΔP by the value ##EQU15## and numeral 8 denotes an addition point whichadds (1) a monitor component ΔSm based on feedback of a plate thicknessdeviation produced from an integrator 10 connected to a thickness guagemonitor 9 and (2) the roll gap control quantity ΔS=ΔS₁ +ΔS₂ includingthe crown control compensation control from the multiplier 7, andsubtracts (3) the roll gap variation ΔS provided from an addition point11.

To the addition point 11 which outputs the roll gap variation ΔS isadded a shift position S in accordance with the pulse signalcorresponding to a vertical displacement of a piston 15 of a wedgeactuating cylinder 14 which is provided from a magnescale 13 serving asa position detector for a wedge 12 namely, the change of the roll gapbetween the upper and lower work rolls (not shown) of a mill body 16.Further, an initial roll gap S₀ from a setting unit 17 for setting aneutral position of the roll gap is subtracted from the shift position Sin the addition point 11.

Numeral 18 denotes a hydraulic servo valve which is controlled inaccordance with the output of the addition point 8. The wedge actuatingcylinder 14 is driven by oil pressure supplied through the servo valve18, thereby actuating the wedge 12 to increase or decrease the initialroll gap S₀.

Numeral 19 denotes a multiplier for multiplying the roll gap variationΔS from the addition point 11 by the influence coefficient ##EQU16##provided from a calculation means. The result of this multiplication isinputed to the addition point 6.

Under the above construction, when the incoming-side plate thickness H₁undergoes a change of ΔH, there is provided the rolling load variationΔP from the addition point 3. This rolling load variation ΔP and##EQU17## ΔS provided from the multiplier 19 (namely, the rolling loadvariation ΔP') are added to the addition point 6, while the rolling loadvariation ΔP" detected under crown control is subtracted. Further, therolling load variation ΔP taken out from the addition point 6 ismultiplied by the value ##EQU18## at the multiplier 7, and the result isoutput to the addition point 8.

At the addition point 8, the monitor component ΔSm which is providedfrom the thickness gauge monitor 9 side, the constant gap controlcomponent ΔS₁ +ΔS₂ provided from the multiplier 7, and the roll gapvariation ΔS provided from the addition point 11 are added, and a signalcorresponding to the roll gap shown in the equation (12) is fed to theservo valve 18 to cause the wedge actuating cylinder 14 to operate sothat the plate thickness on the outgoing side is kept constant even whenthe incoming-side plate thickness changes, with such roll gap correctionquantity as a target.

Thus, according to the crown control compensation controlling method ina multiple roll mill of the present invention, the variation of rollingload caused by crown control is obtained from a crown control quantity,and a wedge type hydraulic reduction device is operated according tosuch rolling load variation to thereby cancel the rolling loadvariation. Consequently, an automatic gauge control and an automaticflatness control can be effected simultaneously while preventing a platethickness variation caused by crown control, thus permitting automationof a multiple roll mill as well as improvement of the plate thicknessaccuracy and shape quality of rolled products.

What is claimed is:
 1. A crown control compensation controlling methodfor controlling the position of at least one wedge in a multiple rollmill, said method comprising the steps of:(a) detecting and storing aninitial value P₀ of a rolling load; (b) detecting the instantaneousvalue P of the rolling load; (c) calculating the instantaneous rollingload variation ΔP by subtracting the initial value P₀ of the rollingload from the instantaneous value P of the rolling; (d) multiplying thecrown control quantities ΔC₁, ΔC₂, . . . ΔC_(n) at preselected controlpoints by the coefficients of influence on rolling load L₁, L₂, . . .L_(n) and summing the products to obtain a rolling load variation ΔP";(e) multiplying the instantaneous rolling load variation ΔP by the value##EQU19## wherein M is the mill modulus of the rolling mill and m is theplasticity modulus of the rolling stock, thereby obtaining a value ΔS₁+ΔS₂ =ΔS, wherein ΔS is the roll gap control quantity and ΔS₁ and ΔS₂are two portions into which the roll gap control quantity ΔS is divided;(f) multiplying the roll gap control variation ΔS by an influencecoefficient ##EQU20## wherein M and m are as defined previously toobtain the secondary rolling load variation ΔP'; (g) adding theinstantaneous rolling load variation ΔP and a secondary rolling loadvariation ΔP' and subtracting the rolling load variation ΔP" to obtainthe instantaneous rolling load variation caused by entry plate thicknessvariation ΔP; (h) measuring the instantaneous plate thickness; (i)calculating the plate thickness variation ΔP; (j) calculating a monitorcomponent ΔS_(m) based on feedback of the plate thickness deviation; (k)subtracting the initial roll gap S₀ between the upper and lower workrolls from the shift position S of the work rolls to obtain the roll gapvariation ΔS; (l) adding the monitor component ΔS_(m) to the roll gapcontrol quantity ΔS=ΔS₁ +ΔS₂ and subtracting the roll gap variation ΔS;and (m) controlling the position of at least one wedge in accordancewith the value of the roll gap control quantity ΔS=ΔS₁ +ΔS₂.